ABSTRACT
The average fraction of parts that are nonconforming in the output of a process while it is under control is one of the three critical pieces of data to be used in decision calculations: to test or not to test. When the process is detected by SPC to be out of control, the process must be stopped, the parts made during the run rule must be quarantined, and those parts must be tested 100%. The decision about testing
all
parts
all
the time depends upon
the proportion nonconforming parts made while the process is under control. This proportion is found in retrospect over extended periods of time while the process was in control.
